DW1000 User Manual
© Decawave Ltd 2017
Version 2.12
Page 57 of 242
External Clock
38.4 MHz
SYNC
124.8MHz
WAIT Cycles wrt
EXT_CLK
TX START
Figure 24: Synchronised Transmission
6.1.3 One Shot Receive Synchronisation (OSRS) Mode
One Shot Receive Synchronisation (OSRS) mode provides a second timebase in DW1000 that can be
synchronised to an external timebase and used to timestamp receive events. This allows a user to have a
timebase outside the DW1000, and to receive timing information about the receive events in this timebase.
OSRS mode is configured by setting the OSRSM bit in the EC_CTRL register, see
Register file: 0x24 – External
. A 1 GHz clock for an offset counter, EC_GOLP, must also be activated in this mode,
by setting the PLLSYN field (bit 15) in the PMSC_CTRL1 register, see
Sub-Register 0x36:04 – PMSC_CTRL1
In normal operation, a ranging timestamp is calculated based on the DW1000 internal timebase; see section
. The timebase counter is captured at the receive event, RMARKER, and a
number of offset values are combined with this capture value to give the ranging timestamp.
When timestamping the receive event relative to an external timebase, the procedure is similar to the
normal method except that an offset is introduced to compensate for the error introduced by the use of the
internal 125 MHz clock to capture a value on the external 38.4 MHz clock domain. As in normal operation,
these offsets and captured values are combined to give the ranging timestamp.
N-1
N
N+1
T
2
T
1
External Clock
38.4 MHz
Cycle Counter
(RX_TS_EST)
RMARKER
1GHz Offset Counter
(OFFSET_EXT)
N
Time Stamp
Figure 25: OSRS Mode Receive Timebase Synchronisation
Now the timestamp in the external timebase may be computed as:
T
rx
= N×T
External
+T
2
+T
3
.